The present invention relates to a controller for an internal combustion engine.
An internal Combustion engine includes in-cylinder injection valves, a supply passage, and a high-pressure fuel pump. Each in-cylinder injection valve includes a coil that opens the valve when energized to inject fuel into a corresponding combustion chamber of the internal combustion engine, The supply passage supplies fuel to the in-cylinder injection valves. The high-pressure fuel pump supplies pressurized fuel to the supply passage. Japanese Laid-Open Patent Publication No. 2014-238047 describes a device that applies a valve-opening voltage to a coil incorporated in an in-cylinder injection valve in order to increase the current flowing to the coil. Then, a holding voltage, which is smaller than the valve-opening voltage, is intermittently applied to the coil so that the current flowing to the coil has a holding current value. In particular, the device switches from the valve-opening voltage to the holding voltage when the current flowing through the coil reaches a predetermined peak value.
To ensure that the fuel injection valve opens and injects fuel, the required current value is higher when the fuel pressure of a delivery pipe (supply passage) that supplies fuel to the in-cylinder injection valves is high than when the fuel pressure of the delivery pipe is low. Accordingly, in the above device, a larger peak value is set as the detected fuel pressure value increases. Further, when the value (pressure difference) obtained by subtracting the detection value of the fuel pressure from a target fuel pressure value increases, a larger peak value is set. This is because fluctuations in the fuel pressure are larger if the high-pressure fuel pump discharges a large amount of fuel to the delivery pipe when the pressure difference is large than when the pressure difference is small. More specifically, the maximum value of the fuel pressure is greater when fluctuations in the fuel pressure are large than when the fluctuations in the fuel pressure are small. Thus, when the fuel pressure has a large maximum value because the pressure difference is large, a larger current value is required to enable fuel injection with the in-cylinder injection valves. Thus, a large peak value is also set in such a case to enable the injection of fuel.
The high-pressure fuel pump is operated so that the fuel pressure detected to set the peak value converges on a target fuel pressure. Even when the pressure difference of the fuel pressure and the target fuel pressure is the same, the maximum value of the fuel pressure differs in accordance with whether or not the fuel pressure is converged on the target fuel pressure. Thus, even when the pressure difference is the same, the necessary lower limit current value required to enable fuel injection with the in-cylinder injection values differs in accordance with whether or not the fuel pressure is converged on the target fuel pressure. However, in the device described above, the peak value is set regardless of whether or not the fuel pressure is converged on the target fuel pressure. Thus, the peak value may be set to a value that is larger than necessary. As a result, a drive circuit of the in-cylinder injection valves may require a large thermal rating.